Trash accumulation in aquatic ecosystems is a growing environmental concern in part because of how chemical and physical effects of trash can harm primary producers such as biofilms. The food webs in aquatic ecosystems like streams are supported by biofilms, communities of algae and other microorganisms growing on substrates in the water. Biofilms play a crucial role in stream ecosystems by contributing to nutrient cycling and organic matter processing, yet their growth is dependent on access to nutrients and stable surfaces for attachment. Trash in urban streams can be a substrate for biofilms to grow when natural cobbles and wood are buried by sediment. This study investigated how biofilm growth and metabolism differ when stream biofilms colonize various types of trash. We found that biofilm growth and metabolic activity differed significantly among trash substrate types. Gross primary production (GPP) varied across substrates (p = 0.0014), with more textured materials, including avocado, fritted glass, and plastic bottles, supporting the highest GPP, while smooth plastic film supported the lowest. Community respiration also differed strongly by substrate (p = 4.56 × 10-6), with organic materials such as avocado and cardboard exhibiting higher oxygen consumption than plastic substrates. Biofilm biomass (AFDM) differed significantly among substrates (p = 0.0001), with avocado accumulating the greatest biomass and plastic film the least. Areal chlorophyll-a density showed weaker substrate effects (p = 0.087), though fritted glass supported higher chlorophyll-a than smoother plastics. Across substrates, GPP was positively related to AFDM, though this relationship was not statistically significant (p = 0.1338). Overall, textured and organic substrates supported greater biofilm biomass and metabolic activity than smooth plastics, indicating that surface properties and material composition strongly influence biofilm colonization and function in urban streams.